The maximum deflection of a row of blades of a turbomachine and thus its aerodynamic load capacity are limited, for one thing, by a separation of the flow along the blade profile. For another thing, the maximum deflection is limited by a separation of a boundary-layer flow on the side walls on the hub side and on the housing side. Double-row and multiple-row blade groups are known for purposes of increasing the deflection capacity of rows of blades. Examples of double-row blade groups are shown in FIG. 1. Other double-row blade groups are described by way of an example in German patent application DE 10 2009 013 399 A1 as well as in European patent specification EP 0 823 540B1.
The blade-row groups shown in FIG. 1 are a blade-row group 2 on the rotor side, a blade-row group 4 on the stator side, and a variable blade-row group 6. The blade-row groups 2, 4, 6 are each formed by a plurality of blade group arrangements that are configured as familiar tandem blade arrangements, each having two blades 8, 10 arranged one after the other in the flow direction. The front blades 8 and the rear blades 10 each form a blade row.
The blade-row group 2 on the rotor side and the blade-row group 4 on the stator side are each firmly joined to a hub 12 or to a housing 14, whereby a tight clearance 16 is formed between the tips of the blades 8, 10 and the housing 14 or the hub 12. The blades 8, 10 of the variable blade-row group 6 are each mounted at their ends on a rotary disk 18, 20 and can be pivoted around a transversal axis 22 as depicted by the arrow indicating the rotation. The blades 8, 10 can be at a distance from each other in the axial direction (blade-row group 2 on the rotor side and variable blade-row group 6) or else can form an overlapping area 24 (blade-row group 4 on the stator side).